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Device Storage

Brief purpose of API: Let content access files based on name and type. Can be enumerated.

Inherent threats:

  • Use excessive resources (file space), read files, change or delete files.
  • Files could potentially contain confidential information.
  • Create files with incriminating / illegal information, then call the cops
  • Create files that other apps can look for to control their behavior

Threat severity: high to critical - privacy concerns, loss of user data, access to confidential data.


Type Use Cases Authorization Model Notes & Other Controls
Web Content None No direct access (access via web activities)
Installed Web Apps None No direct access (access via web activities)
Privileged Web Apps Photo gallery, camera app that displays photos, any app that saves data will likely want to read it back. Explicit
  • Granting permission only for a particular type of file (images, pdf, etc).
  • In the short run we will rely on the "intended usage" to communicate to the user the risk of permitting this access.
Certified Web Apps Notify an app if the user is idle. Implicit


Ideally permission should be given on a type basis (i.e. enforce the "intended usage" at runtime). So giving permission to access music doesn't automatically give permission to photos. If the type is a string literal when the code is reviewed, that would mitigate the issue. Otherwise sub-permissions for types (device-storage.music) or separate permissions for each type (device-storage-music) would be needed. Also has the benefit that it allows the permission prompt to be more explicit about what is being granted.